Integrated circuit with a titanium nitride contact barrier having oxygen stuffed grain boundaries

ABSTRACT

Methods of forming, in an integrated circuit, aluminum-silicon contacts with a barrier layer is disclosed. The barrier layer is enhanced by the provision of titanium oxynitride layers adjacent the silicide film formed at the exposed silicon at the bottom of the contact. The titanium oxynitride may be formed by depositing a low density titanium nitride film over a titanium metal layer that is in contact with the silicon in the contact; subsequent exposure to air allows a relatively large amount of oxygen and nitrogen to enter the titanium nitride. A rapid thermal anneal (RTA) both causes silicidation at the contact location and also results in the oxygen and nitrogen being gettered to what was previously the titanium/titanium nitride interface, where the oxygen and nitrogen react with the titanium metal and nitrogen in the atmosphere to form titanium oxynitride. The low density titanium nitride also densifies during the RTA. Alternative embodiments are also disclosed in which the silicide is formed first, prior to the formation of additional titanium oxynitride by air exposure and RTA, or by sputter deposition. Each of these processes produces a high-quality barrier contact structure overlying a silicide film, where the barrier structure includes titanium oxynitride and titanium nitride.

This is a Continuation of application Ser. No. 08/235,099, filed Apr.29, 1994, now U.S. Pat. No. 5,514,908.

This invention is in the field of integrated circuits, and is morespecifically directed to processes for forming metal-to-semiconductorcontacts in the same.

BACKGROUND OF THE INVENTION

In the field of integrated circuit manufacture, particularly with thecontinuing trend toward smaller integrated circuit feature sizes, themaking of high-reliability conductive electrical contacts betweenmetallization layers and semiconductor elements, particularly contactsbetween aluminum and diffused junctions into single-crystal silicon, hasbecome more difficult. This increased difficulty is due to the tendencyfor aluminum and silicon to interdiffuse when in contact with oneanother, and when subjected to the high temperatures necessary forintegrated circuit manufacturing. As is well known in the art,conventional integrated circuit process steps can cause aluminum atomsto diffuse from a metal electrode of pure aluminum into single-crystalsilicon to such a depth as to short out a shallow p-n junction in thesilicon; this phenomenon is known as junction spiking. The use ofsilicon-doped aluminum in forming integrated circuit metallization,while preventing junction spiking, is known to introduce thevulnerability of the contact junction to the formation of siliconnodules thereat, such nodules effectively reducing the contact area, andthus significantly reducing the conductivity of the contact.

Accordingly, recent advances in the field of integrated circuitfabrication have been made by the introduction of so-called "barrier"layers at the aluminum-silicon contact. Conventionally, the barrierlayer is a refractory metal compound such as titanium-tungsten (TiW), ora refractory metal nitride such as titanium nitride (TiN). The barrierlayer is formed at the contact locations so as to be disposed betweenthe silicon and the overlying aluminum layer. In some cases, the barrierlayer is formed by deposition of the refractory metal, followed by ananneal which forms both the barrier layer compound and also a metalsilicide where the metal is in contact with the silicon; as is known inthe art, the metal silicide improves the conductivity of the contact. Inany case, the barrier layer inhibits the interdiffusion of aluminum andsilicon atoms, thus eliminating the problems of junction spiking andsilicon nodule formation noted above.

Other techniques for improving the barrier properties of TiN layers haveincluded the enhancement of the barrier by manipulating and controllingparameters in the deposition of the TiN film. U.S. Pat. No. 4,976,839,issued Dec. 11, 1990 and incorporated hereinto by reference, disclosesthat the presence of an oxide at grain boundaries within a titaniumnitride film improves the ability of the film to prevent the mutualdiffusion of silicon and aluminum therethrough. This reference alsodiscloses a method for forming a titanium nitride barrier layer havinglarge grain sizes by increasing the substrate temperature duringsputtering, so that the formation of oxides at the grain boundaries maybe accomplished with a relatively large amount of oxygen present, butwithout degradation in the conductivity of the film. Such control ofsubstrate temperature to enhance the TiN barrier is also described inInoue et al., Proceedings of IEEE VLSI Multilevel InterconnectConference, (IEEE, 1988) p.205 et seq. TiN deposition parameters otherthan substrate temperature have also been controlled in efforts toenhance the barrier properties of the film. These parameters includedeposition pressure and substrate bias voltage. Each of these priortechniques have been directed to deposit a more densified, orcrystallized, TiN film, with the intent that the film has improvedbarrier properties.

Other known techniques for enhancing TiN barrier properties haveincluded the use of post-deposition treatments of the film by stuffingthe TiN film with oxygen. Sinke et al., Appl. Phys. Lett., Vol. 47, No.5, (1985) p. 471 et seq., describes the use of air exposure as such atreatment. Dixit et al., Appl. Phys. Lett., Vol. 62, No. 4, (1993) p.357 et seq., describes the use of rapid thermal anneal (RTA) as anotherpost-deposition treatment of TiN film.

It is an object of the present invention to provide a method of formingan integrated circuit in which a barrier layer at contact locations maybe formed in such a manner as to provide excellent interdiffusionbarrier properties.

It is a further object of the present invention to provide such a methodthat is useful in extremely small contact openings, including those ofbelow one micron.

It is a further object of the present invention to provide such a methodthat has a high degree of process robustness.

Other objects and advantages of the present method will be apparent tothose of ordinary skill in the art having reference to the followingspecification together with the drawings.

SUMMARY OF THE INVENTION

The invention may be incorporated into a method of fabricating anintegrated circuit that includes the formation of barrier layers atcontact locations. After the formation of the contact opening throughthe dielectric opening to expose silicon at the contact locations, thepresent invention forms a titanium silicide layer at the exposed siliconover which a titanium nitride film is formed, and where a titaniumoxynitride layer is formed between the titanium silicide and thetitanium nitride. According to one aspect of the invention, a poroustitanium nitride layer is formed over the titanium metal from which thesilicide is to be formed. Exposure of the wafer to an oxygen-bearingatmosphere (including air) after formation of the porous titaniumnitride allows oxygen to enter the film; subsequent rapid thermal annealcauses both silicidation at the silicon-titanium interface, and alsocauses the titanium nitride to densify into a high density film with atitanium oxynitride layer at the silicide/nitride interface.

According to another aspect of the invention, the titanium metal may besputtered and followed by deposition of a titanium oxynitride film, insitu with the metal sputtering; a titanium nitride film may then beformed over both, optionally followed by RTA. This aspect of theinvention enables the sputtering of the barrier layer in situ with themetal deposition, reducing handling of the wafers.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1a through 1e are cross-sectional views of a partiallymanufactured integrated circuit illustrating steps of a fabricationprocess according to a first preferred embodiment of the invention.

FIG. 2 is a plan view of the integrated circuit of FIGS. 1a through 1e,shown after the step corresponding to FIG. 1e.

FIGS. 3a through 3f are Auger electron spectroscopy results for six testgroups in an experimental verification of the mechanism by way of whichthe first embodiment of the invention provides improved barrierprotection.

FIG. 4 is a plot of thermal stress hours versus diode failure percentagefor the six test groups of FIGS. 3a through 3f.

FIGS. 5a through 5c are cross-sectional views of a partiallymanufactured integrated circuit illustrating steps of a fabricationprocess according to a second preferred embodiment of the invention.

FIGS. 6a and 6b are cross-sectional views of a partially manufacturedintegrated circuit illustrating steps of a fabrication process accordingto a third preferred embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to FIGS. 1a through 1e, a method of fabricating anintegrated circuit to have a barrier layer at its contact openingsaccording to a first embodiment of the invention will now be describedin detail. The cross-sections of FIGS. 1a through 1e illustrate thismethod as a portion of an overall process flow for fabricating theintegrated circuit. As will be apparent to those of ordinary skill inthe art, the partial process flow to be described herein may be appliedin the fabrication of many types of integrated circuits, in which thefull process flow will include many other process steps conventional inthe art.

FIG. 1a illustrates, in cross-section, a portion of an integratedcircuit that has been partially fabricated. According to the exampledescribed herein, the present invention is directed to forming a barrierlayer between an aluminum metallization layer and a doped semiconductorregion in single-crystal silicon, as such contacts are generally themost sensitive to the spiking and nodule problems addressed by barrierlayers. It is contemplated, of course, that the present invention willalso be applicable to the formation of other contacts, including, forexample, contacts between metallization and polysilicon.

The structure of FIG. 1a includes silicon substrate 2, into a surface ofwhich doped diffusion region 4 is formed, of opposite conductivity typefrom that of substrate 2. For example, substrate 2 may be lightly dopedp-type silicon and diffusion region 4 may be heavily doped n-typesilicon. Of course, as noted above, other structures (with the same oropposite conductivity type selection) may alternatively be used; forexample, substrate 2 may instead be a well or tub region in a CMOSprocess, into which diffusion 4 is formed. In the example of FIG. 1a,diffusion 4 is bounded by field oxide structure 6, formed in theconventional manner. In this example, diffusion 4 is very shallow, suchas on the order of 0.15 microns, as is conventional for modernintegrated circuits having sub-micron feature sizes. As such, diffusion4 may be formed by ion implantation of the dopant followed by ahigh-temperature anneal to form the junctions, as is well known in theart; alternatively, the ion implantation may be performed prior to theformation of subsequent layers, with the drive-in anneal performed laterin the process, if desired.

Dielectric layer 8, which may be a deposited oxide or another type ofdielectric layer, is formed over diffusion 4 and field oxide 6, forpurposes of electrically isolating overlying conductive structures fromdiffusion 4, except at locations where contacts therebetween aredesired. In FIG. 1a, contact opening 9 has been formed throughdielectric layer 8, for example by way of reactive ion etching oranother type of anisotropic etching; as will be apparent below, thisembodiment of the invention is concerned with the formation of anoverlying metallization and barrier structure that is in contact withdiffusion 4 through contact opening 9. In this example, contact opening9 may be as small as less than one micron in width, as is typical formodern sub-micron integrated circuits.

Each of the structures illustrated in FIG. 1a may be formed according toconventional process steps in the art of integrated circuit manufacture.

After completion of the structure illustrated in FIG. 1a, a thin layer10 of titanium metal is deposited overall, resulting in the structureillustrated in FIG. 1b. Titanium layer 10 is preferably formed by way ofsputtering, to a thickness of on the order of 300 to 1000 Å; thethickness of titanium layer 10 is selected according to the thickness ofthe silicide layer that is to be formed at the contact location (as willbe described in detail below). In this example, the thickness oftitanium layer 10 is approximately 600 Å.

Following the formation of titanium layer 10, a layer 12 of titaniumnitride is then formed overall, resulting in the structure of FIG. 1c.According to this embodiment of the invention, titanium nitride layer 12is intentionally formed to have a relatively low density. The preferredmethod for the deposition of titanium nitride layer 12 is by way ofreactive sputtering, in which titanium metal is sputtered in anitrogen-bearing atmosphere under temperature, pressure and biasconditions that enables the reaction of the sputtered titanium ions withthe nitrogen in the atmosphere. The low density of titanium nitridelayer 12 is created by proper selection of the substrate temperature andthe sputtering chamber pressure. For example, reactive sputtering oftitanium nitride at relatively cool substrate temperatures of on theorder of 100° C. and at relatively weak vacuum conditions (on the orderof 10 mTorr), has been found to provide quite a low density film oftitanium nitride. This is in contrast to conventional high densitytitanium nitride, which is sputtered at substrate temperatures on theorder of 300° C. and vacuums of at most 4 mTorr to provide the largegrain sizes and high density desired in the prior art. As a result ofthe sputtering conditions according to this first preferred embodimentof the invention, low density titanium nitride film 12 is thereforequite porous at this stage of the process. The thickness of titaniumnitride layer 12 is on the order of 300 to 1000 Å according to thisembodiment of the invention; a preferred thickness of titanium nitridelayer is approximately 1000 Å, for a particular application.

It is preferred that titanium nitride layer 12 may be formed in situwith the sputtering of titanium layer 10, with the temperature, pressureand atmosphere being changed upon completion of the titanium layer 10.Alternatively, the sputtering of titanium nitride layer 12 may beperformed in a different processing chamber from the sputtering oftitanium layer 10, as desired. After the deposition of titanium nitridelayer 12, it is also preferred to sputter a thin (e.g., 200 Å) layer oftitanium metal (not shown) thereover in order to clean the sputteringtarget; if used, this additional titanium layer will later react to formtitanium nitride, and as such will not significantly change theresulting structure.

Following the deposition of titanium nitride layer 12, the structure isremoved from the processing chamber and exposed to an oxygen-bearingatmosphere, and preferably an atmosphere such as air that bears bothoxygen and nitrogen. It is believed that the oxygen molecules in theatmosphere (and also nitrogen molecules, if present) diffuse intotitanium nitride layer 12 along its grain boundaries. The low densitytitanium nitride layer 12 formed as described above ensures suchinfiltration of oxygen (and nitrogen) thereinto during this exposure, incontrast to conventionally formed titanium nitride layers having highdensity and large grain sizes, in which the infiltration of oxygen andnitrogen is inhibited. It has been observed that the infiltration ofoxygen into low density titanium nitride layer 12 occurs substantiallyimmediately (i.e., on the order of a few minutes), with longer exposuresnot having a significant effect on the eventual film. As such, the timeand conditions of the air exposure of titanium nitride layer 12 are notat all critical.

Following the air exposure of titanium nitride layer 12, the structureundergoes an anneal, preferably a rapid thermal anneal (RTA), in orderto form an underlying silicide at the bottom of contact opening 9 and toreact the infiltrated oxygen and nitrogen with titanium layer 10, at theinterface between titanium layer 10 and titanium nitride layer 12. RTAis preferred for this step, to minimize oxidation of the elementaltitanium metal in layer 10. It has been observed that the specificconditions of the RTA are not believed to be critical, so long as theRTA is adequate to direct react the titanium layer 10 at the locationsadjacent diffusion region 4 to form titanium disilicide (TiSi₂) thereat.The RTA also densifies titanium nitride layer 12 to a more compactstructure. An example of RTA useful according to this embodiment of theinvention is a 650° C. anneal in nitrogen ambient, for 30 seconds.

FIG. 1d illustrates the exemplary structure after the RTA process hasbeen performed. Titanium disilicide layer 16 is formed at the exposedportion of diffusion 4, which was previously in contact with titaniumlayer 10; assuming selection of the proper thickness of titanium layer10, the consumption of silicon of diffusion 4 in the formation ofsilicide layer 16 is limited, so that silicide layer 16 does not extendthrough diffusion 4 and short out the junction between diffusion 4 andsubstrate 2.

As shown in FIG. 1d, as a result of the air exposure of low densitytitanium nitride layer 12 prior to RTA, and the infiltration of oxygenthereinto during such exposure, titanium oxynitride (TiON) layer 18 isformed at what was previously the interface between titanium layer 10and titanium nitride layer 12, both at locations in contact withsilicide layer 16 and also over dielectric layer 8. It is believed thatTiON layer 18 is formed by oxygen gettering at this interface duringRTA, with the oxygen reacting with titanium layer 10 and availablenitrogen thereat to form the TiON compound. It is believed that theportion of titanium nitride layer 12 nearest to titanium layer 10 willbe somewhat depleted of oxygen, which is gettered to thetitanium/titanium nitride interface. The particular stoichiometry of thetitanium oxynitride will vary according to the particular conditions,such that the layer 18 can, at best be referred to as TiO_(x) N_(y). Thethickness of titanium oxynitride layer 18 is, in this example, on theorder of 100 to 300 Å.

The thickness of titanium nitride layer 12 is preferably limited to thatwhich ensures that the full thickness of titanium layer 10 overdielectric layer 8 reacts, during the RTA, to form either titaniumsilicide or the titanium oxynitride compound. It is undesirable forelemental titanium to remain in the film at this point, as thiselemental titanium would oxidize during subsequent process steps.

It has also been observed that the upper portion of titanium nitridelayer 12 is "stuffed" with oxygen as a result of the air exposurefollowed by RTA; this stuffed region is illustrated in FIG. 1d by layer12'. In this example, the thickness of oxygen-stuffed titanium nitridelayer 12' is on the order of 300 to 500 Å.

As shown in FIG. 1e, following the RTA step, aluminum metallization 20may be evaporated or sputtered over the structure to the desiredthickness. Aluminum layer 20 may consist of pure aluminum, or aluminumdoped with silicon or copper, as is conventional in the art. In thisexample, the thickness of aluminum layer 20 may be on the order of 4000to 8000 Å. Following the deposition of aluminum layer 20, conventionalpatterning and etching of the stack of titanium oxynitride 18, titaniumnitride 12, 12', and aluminum layer 20 is performed as conventional inthe art to form the conductors desired in the particular integratedcircuit. FIG. 2 illustrates, in plan view, the portion of the integratedcircuit structure of FIG. 1e; the location of contact opening 9 and theinner edges of titanium nitride layer 12 are shown in shadow in the planview of FIG. 2.

According to this embodiment of the invention, the barrier formed by thestructure of titanium oxynitride layer 18, titanium nitride layer 12,and oxygen-stuffed titanium nitride layer 12' has been observed to be ofhigh quality and integrity. Indeed, experiment has shown that thebarrier structure according to the present invention, when applied todiode test structures, results in a lower percentage of reverse biasdiode leakage failures after thermal stress at 450° C., as compared withsimilarly sized diodes having conventional barrier layers such as highdensity titanium nitride disposed over titanium metal (both subjected toRTA and not subjected to RTA).

It is believed that the improved barrier performance provided by thestructure according to this embodiment of the invention is due to theformation of titanium oxynitride layer 18 at what was the interfacebetween titanium layer 10 and low density titanium nitride layer 12. Theformation of this layer, according to this embodiment of the invention,was enabled by the low density nature of titanium nitride layer 12 asdeposited, which is stuffed with oxygen 12 during the exposure of thestructure to air or another oxygen-bearing atmosphere, after deposition.During the subsequent RTA operation, this stuffed oxygen is gettered bytitanium layer 10, and reacts thereat to form TiON layer 18.

EXPERIMENTAL RESULTS

Single-crystal p-type silicon wafers were processed with conventionalCMOS technology, to fabricate n+/p test diode strings for investigationof this first embodiment of the invention. The diode strings includedshallow n+ diffusion regions formed by an arsenic implant (3×10¹⁵ doseat 60 KeV), a phosphorous implant (3×10¹⁴ dose at 65 KeV), and a 900° C.furnace anneal for thirty minutes to form the junctions. After oxidedeposition, one micron contacts were made to the diffused regions, to beconnected in parallel (in groups of 10⁵ diodes), each diode having anarea of 0.0635 cm².

To investigate the mechanism of the formation of the TiON layerdescribed above, six barrier/metal structure schemes were compared. Eachtest group first received 550 Å of sputtered titanium. Three groupsreceived low density sputtered titanium nitride film (500 Å) produced asdescribed above relative to this embodiment of the invention, and threegroups received high density sputtered titanium nitride film (500 Å) inthe conventional manner. Aluminum was deposited over each test group,either in situ, after an air break, and after both an air break and anRTA anneal at 650° C. The six test groups may be summarized as follows:

a) Ti/low density TiN/in situ Al

b) Ti/high density TiN/in situ Al

c) Ti/low density TiN/Al after air break

d) Ti/high density TiN/Al after air break

e) Ti/low density TiN/Al after air break and RTA

f) Ti/high density TiN/Al after air break and RTA

Group (e) corresponds to the first preferred embodiment of the inventiondescribed hereinabove relative to FIGS. 1a through 1e, and FIG. 2.

The low density and high density nature of the titanium nitride filmswas confirmed by electrical conductivity measurements (low density TiNhaving average resistivities of 1120 μohm-cm and 1640 μohm-cm after airbreak, but before and after RTA, respectively; high density TiN havingaverage resistivities of 90 μohm-cm after air exposure both before andafter RTA).

X-ray diffraction measurements of the six groups of film also confirmedthat the low density TiN film indeed had low density as deposited, basedon d-spacing measurements. These x-ray diffraction measurements alsoindicated that low-density TiN, formed according to the first preferredembodiment of the invention, densifies when subjected to RTA into ahigher density than that of conventional high density TiN. These resultsare shown in the following table of the six test groups indicated above,where "d" is the measured lattice constant for the specified materialand plane, and where "ratio" is the ratio of the measured latticeconstant for the group relative to the ideal lattice constant for thespecified material and plane:

                  TABLE 1    ______________________________________           Ti(002)    Ti(011) TiN(111)    ______________________________________    Group (a): Ti/low density TiN/in situ Al    d        2.346        --      2.464    (ratio)  (1.002)      --      (1.010)    Group (b): Ti/high density TiN/in situ Al    d        2.342        2.243   2.457    (ratio)  (1.000)      (1.000) (1.007)    Group (c): Ti/low density TiN/Al after air break    d        2.346        --      2.469    (ratio)  (1.002)      --      (1.012)    Group (d): Ti/high density TiN/Al after air break    d        2.343        2.243   2.455    (ratio)  (1.001)      (1.000) (1.006)    Group (e): Ti/low density TiN/Al after air break and RTA    d        2.387        --      2.431    (ratio)  (1.019)      --      (0.996)    Group (f): Ti/high density TiN/Al after air break and RTA    d        2.375        2.255   2.444    (ratio)  (1.014)      (1.005) (1.002)    ______________________________________

As is evident from the table, the low density TiN film of groups (a) and(c), which have not been subjected to RTA, in fact have relatively largeTiN(111) lattice constants (ratios of 1.010 and 1.012, respectively),relative to those of high density TiN films of groups (b) and (d) thathave undergone similar processing without RTA (ratios of 1.007 and1.006, respectively). However, the data in the Table clearly shows thatthe TiN film of group (e), which is of low density as deposited, isdensified by the RTA to a higher density and lower lattice constant(ratio of 0.996) than that of the high density (as deposited) TiN filmof group (f) that is subjected to RTA (ratio of 1.002). This dataindicates the additional benefit of this first preferred embodiment ofthe invention, in that a higher density TiN film is obtained by the RTAprocessing of a TiN film that has a low density as deposited.

Referring now to FIGS. 3a through 3f, Auger electron spectroscopy (AES)analysis of the barrier structures (i.e., below aluminum) formedaccording to the six test groups (a) through (f), respectively, areshown. For groups (a) and (b) shown in FIGS. 3a and 3b, respectively, inwhich aluminum was deposited in situ with the Ti/TiN films, oxygen isnot present to a significant degree in either group. Referring to FIGS.3c and 3d, where aluminum is deposited after exposure to air (an airbreak), a significant degree of oxygen is present in the low density TiNgroup (c), while no significant amount of oxygen is evident in the highdensity TiN group (d); in addition, FIG. 3c illustrates that thenitrogen concentration within the low density. TiN film of group (c) ishigher, at locations deeper into the film, than that of the high densityTiN film of group (d). FIGS. 3c and 3d thus indicate that the lowdensity TiN film formed according to the first embodiment of theinvention is stuffed with much more oxygen, and also with more nitrogen,than is the high density TiN film, after exposure of the wafers to air(and before RTA). The presence of more oxygen in the low density TiNfilm is evident by the higher resistivities noted above.

Referring now to FIG. 3e, the AES results of the barrier structureaccording to the first embodiment of the invention, after RTA, isillustrated; FIG. 3f shows, for comparison, the AES results for a highdensity film similarly processed, with RTA after air break and beforealuminum deposition. It is clear from FIG. 3e that the oxygen stuffedinto the TiN film has been gettered at the Ti/TiN interface by the RTAtreatment, as indicated by the oxygen peak highlighted by the arrow inFIG. 3e and by the depletion of oxygen from the portion of the filmimmediately above this peak (seen by comparing FIGS. 3c and 3e). Thisoxygen gettering is also evident in the high density TiN group (f) inFIG. 3f; however, since less oxygen and less nitrogen are stuffed intothe high density TiN film as shown in FIG. 3d, it is believed that theTiON formed at the Ti/TiN interface for this structure will be muchthinner. Greater oxygen gettering has therefore occurred at the Ti/TiNinterface of the low density TiN film group (e), after RTA, resulting ina high integrity layer of TiON thereat, and improved barrierperformance. FIG. 3e also illustrates that the upper portion of the TiNlayer is stuffed with oxygen, given the relatively high level of oxygenappearing in the AES results thereat.

The enhanced reaction of nitrogen and oxygen with the titanium metalobtained by this first embodiment of the invention also has the benefitof limiting the silicide thickness, by reducing the amount of elementaltitanium available for silicidation. As such, the present invention isparticularly applicable to integrated circuits having extremely shallowjunctions, where consumption of the junction by the silicidation is ofconcern.

Following fabrication of the six test groups, diode strings in sampleintegrated circuits were subjected to thermal stress at 450° C., and thepercentage of diode failures noted for each group. FIG. 4 is a plot ofthe thermal stress results, with the percentage failure on the verticalaxis and the stress time on the horizontal axis. It is believed that thethermal stress diode leakage test accurately correlates to barrierintegrity, considering that thermal stress accelerates theinterdiffusion of aluminum and silicon at contact locations, withfailure of the diode junction occurring upon aluminum atoms reaching themetallurgical p-n junction through the barrier. As is evident from FIG.4, the TiON layer formed according to the first embodiment of theinvention provides excellent protection to such interdiffusion, relativeto the other test groups, and particularly relative to group (f) havinghigh density TiN and subjected to the air exposure and RTA processes.

Referring now to FIGS. 5a through 5c, a method of forming a barrierstructure in a contact according to a second preferred embodiment of theinvention will now be described in detail. In this embodiment of theinvention, a titanium layer is first deposited over the structure ofFIG. 2a to the desired thickness for formation of the silicide at thecontact location, and as such in contact with diffusion 4 and overlyingdielectric layer 8. According to this embodiment of the invention, thestructure is exposed to air or an oxygen-bearing atmosphere, so thatoxygen stuffs the titanium layer. RTA is then performed in a nitrogenatmosphere, reacting the titanium layer with the silicon surface ofdiffusion 4 to form a silicide thereat, and with the titanium metalreacting with the nitrogen in the atmosphere and also the stuffed oxygenfrom the air break, resulting in a titanium oxynitride compoundelsewhere. The resultant structure is illustrated in FIG. 5a, withsilicide layer 16 formed at the bottom of contact opening 9. Titaniumoxynitride layer 22 is formed elsewhere over dielectric layer 8, andalso at the upper surface of silicide 16, to some extent.

Following the RTA direct reaction of the deposited titanium, andreferring to FIG. 5b, titanium nitride layer 24 is sputtered overtitanium oxynitride layer 22, and titanium metal layer 26 is thensputtered over titanium nitride layer 24. In this embodiment of theinvention, titanium nitride layer 24 may be, and preferably is, ofconventional high density. The thickness of layers 24, 26 are selectedaccording to the particular geometry and, in the case of titanium layer26, considering subsequent processing to ensure that it is fullyreacted. For example, titanium nitride layer 24 has a thicknesspreferably on the order of 500 to 1000 Å, while titanium layer 26 has athickness preferably on the order of 200 to 700 Å. Titanium nitridelayer 24 and titanium layer 26 are preferably sputtered in situ with oneanother, with the nitrogen source being turned off, and the titaniumsputtering continuing, after deposition of titanium nitride layer 24 tothe desired thickness. A low density titanium nitride layer mayoptionally also be sputtered over titanium layer 26, if desired.

After deposition of titanium layer 26, the structure is again exposed toair or another oxygen-bearing atmosphere, so as to stuff titanium layer26 with oxygen. Following the air break, RTA is again performed asbefore (with the particular conditions not being critical), in anitrogen atmosphere, so as to react titanium layer 26 with the stuffedoxygen and the nitrogen ambient to form a titanium oxynitride compound.The resultant structure is illustrated in FIG. 5c, with titaniumoxynitride layer 28 formed overall.

This second preferred embodiment of the invention thus results inmultiple layers of titanium oxynitride in the barrier structure. It iscontemplated that this additional titanium oxynitride layer will furtherenhance the barrier properties of the contact, at a cost of additionalprocess steps.

Upon fabrication of the structure of FIG. 5c, processing may thencontinue with the deposition of aluminum metallization, and patterningand etching, to form the desired metal conductors in the circuit, asbefore. Of course, the process of depositing titanium nitride andtitanium, air break, and RTA may be again repeated prior to aluminumdeposition, if additional titanium oxynitride layers are desired.

Referring now to FIGS. 6a and 6b, a method of forming a contact with abarrier layer according to a third embodiment of the invention will nowbe described in detail. In this embodiment of the invention, a titaniummetal layer is sputtered into contact opening 9 and, after an air break,is exposed to RTA to form silicide film 16 and titanium oxynitride 22,resulting in a structure as shown in FIG. 5a described above. Accordingto this third embodiment of the invention and as shown in FIG. 6a afterthe RTA reaction, titanium metal layer 30 is sputtered overall, followedby the sputtering of low density titanium nitride layer 32 over titaniummetal layer 30. Low density titanium nitride layer 32 is sputtered underconditions similar to those described hereinabove relative to the firstpreferred embodiment of the invention, such as low substrate temperatureand weak vacuum, resulting in small grain size and high porosity in thefilm. As before, the sputtering steps forming titanium layer 30 and lowdensity titanium nitride layer 32 are preferably performed in situ withone another. The resulting structure is illustrated in FIG. 6a.

The structure is then exposed to air or an oxygen-bearing atmosphere sothat oxygen stuffs low density titanium nitride layer 32, in the mannerdescribed hereinabove relative to the first preferred embodiment of theinvention. Following the air break, the structure undergoes RTA innitrogen atmosphere to cause the gettering of the stuffed oxygen at thetitanium/titanium nitride interface, where the stuffed oxygen and theavailable nitrogen react with elemental titanium in layer 30 to form atitanium oxynitride compound thereat. The resulting structure isillustrated in FIG. 6b, where second titanium oxynitride layer 34overlies titanium oxynitride layer 22 that was previously formed, andunderlies titanium nitride layer 32. As described hereinabove, it iscontemplated that low density titanium nitride layer 32 is densifiedduring the RTA, and also is stuffed with oxygen near its surface.

As a result of this third preferred embodiment of the invention, adouble thickness of titanium oxynitride is formed in contact locations,thus further enhancing the barrier presented to later deposited aluminummetallization. After aluminum deposition, of course, patterning andetching will follow to form the desired metal conductors in the circuit,as before. If desired, the deposition of titanium metal and low densitytitanium nitride, air break, and RTA may be repeated again prior toaluminum deposition, if another layer of titanium oxynitride in thebarrier structure is desired.

A fourth preferred embodiment of the invention is also contemplated, inthe formation of a barrier structure incorporating titanium oxynitride.In this fourth preferred embodiment of the invention, titanium metal issputtered overall, in contact with diffusion 4 and dielectric layer 8,exposed to air, and subjected to RTA to form silicide at the bottom ofthe contact opening and titanium oxynitride elsewhere, resulting in thestructure shown in FIG. 5a. According to this fourth embodiment of theinvention, however, titanium oxynitride film is directly sputtered ontothe first titanium oxynitride film formed by RTA; it is contemplatedthat the introduction of a controlled amount of oxygen and nitrogen intothe sputtering system will enable the reactive sputtering of titaniumoxynitride film thereover. This deposition of titanium oxynitride willserve to thicken the barrier layer resulting from the RTA silicidationreaction, and enhance the barrier effects thereat. This embodiment ofthe invention also provides a convenient way in which to form thebarrier structure, without requiring removal of the structure from thesputtering apparatus for additional processing.

According to this fourth embodiment of the invention, after reactivesputtering of the titanium oxynitride layer, an additional layer oftitanium nitride may be sputtered thereover, if desired. This additionaltitanium nitride layer may be, and preferably is, of high density, asthe underlying titanium oxynitride layer has already been formed overthe structure. Whether or not this additional layer is formed, thestructure may be subjected to RTA, if necessary to more completely reactthe titanium oxynitride layer in the structure. Processing may thencontinue with the deposition, patterning and etching of aluminum overthe barrier structure, to form the desired electrical conductors in theintegrated circuit.

In each of the embodiments of the invention described hereinabove, ahigh integrity, high quality barrier layer is produced by theincorporation of titanium oxynitride near the silicide film cladding thesilicon at the bottom of the contact. This compound has been found toprovide excellent barrier properties, as evidenced by the reduced diodefailure rate under thermal stress. The various embodiments of theinvention are directed to novel methods of providing a titaniumoxynitride film of adequate thickness and integrity to provide thedesired barrier performance.

While the invention has been described herein relative to its preferredembodiments, it is of course contemplated that modifications of, andalternatives to, these embodiments, such modifications and alternativesobtaining the advantages and benefits of this invention, will beapparent to those of ordinary skill in the art having reference to thisspecification and its drawings. It is contemplated that suchmodifications and alternatives are within the scope of this invention assubsequently claimed herein.

We claim:
 1. An integrated circuit contact structure, comprising:a dopedsemiconducting region at the surface of a body; a dielectric filmdisposed over the doped region, the dielectric film having a contactopening therethrough; a titanium silicide film disposed at an exposedportion of the doped region in the contact opening; a first titaniumoxynitride film overlying the titanium silicide film in the contactopening; a first titanium nitride film overlying the titanium silicidefilm in the contact opening, wherein the first titanium nitride filmcomprises:a first layer, in contact with the first titanium oxynitridefilm; and a second layer, overlying the first layer, and having a higherconcentration of oxygen than the first layer.
 2. The structure of claim1, wherein the first titanium oxynitride film comprises thermal titaniumoxynitride.
 3. The structure of claim 1, wherein the first titaniumnitride film overlies the first titanium oxynitride film.
 4. Thestructure of claim 3, further comprising a second titanium oxynitridefilm overlying the first titanium nitride film.
 5. The structure ofclaim 4, further comprising a second titanium nitride film overlying thesecond titanium oxynitride film.
 6. The structure of claim 1, furthercomprising a second titanium oxynitride film overlying the firsttitanium oxynitride film.
 7. The structure of claim 1, furthercomprising a metallization layer overlying the first titanium oxynitridefilm and the first titanium nitride film.
 8. The structure of claim 7,wherein said metallization comprises aluminum.
 9. The structure of claim1, wherein the first titanium oxynitride film is formed by reactivesputter deposition.
 10. An integrated circuit contact structure,comprising:a doped semiconducting region at the surface of a body; adielectric film disposed over the doped region, the dielectric filmhaving a contact opening therethrough; a titanium silicide film disposedat an exposed portion of the doped region in the contact opening; afirst titanium oxynitride film overlying the titanium silicide film inthe contact opening; a second titanium oxynitride film overlying thefirst titanium oxynitride film; and a first titanium nitride filmoverlying the titanium silicide film in the contact opening, wherein thefirst titanium nitride film overlies both the first and second titaniumoxynitride films, and comprises:a first layer, in contact with thesecond titanium oxynitride film; and a second layer, adjacent the firstlayer, and having a higher concentration of oxygen than the first layer.11. The structure of claim 10, further comprising:a third titaniumoxynitride film overlying the first titanium nitride film; and a secondtitanium nitride film overlying the third titanium oxynitride film. 12.The structure of claim 10, further comprising metallization layeroverlying the first titanium oxynitride film and the first titaniumnitride film.
 13. The structure of claim 12, wherein said metallizationlayer comprises aluminum.